1. Field of the Invention
The present invention relates to an electromagnetic fuel injection valve mainly used in a fuel supply system for an internal combustion engine, and particularly to an improvement in an electromagnetic fuel injection valve including: a valve seat member having a valve seat at one end; a valve housing coupled at one end thereof to the other end of the valve seat member; a stationary core coupled to the other end of the valve housing; and a valve assembly comprised of a movable core slidably accommodated in the valve housing so that it is opposed to the stationary core, and a valve member connected to the movable core through a rod portion and adapted to cooperate with the valve seat, the valve housing being provided with a guide portion on which the valve assembly is axially slidably carried, the valve assembly having a high-hardness coating formed on its outer peripheral surface contacting the guide portion to provide a wear resistance.
2. Description of the Related Art
In a conventional electromagnetic fuel injection valve, it is already known that a high-hardness coating is formed on an outer peripheral surface of a movable core by hard chromium plating or titanium coating, as disclosed in, for example, Japanese Patent Application Laid-open No. 11-22585.
When the high-hardness coating is formed on the outer peripheral surface of the movable core by hard chromium plating or titanium coating, in minimizing the surface roughness of the coating, the surface roughness Rmax is conventionally limited to about 2 μm.
In the conventional electromagnetic fuel injection valve, when the sliding gap between the valve assembly and the guide portion is minimized with their dimensional accuracies enhanced in order to stabilize the opened and closed attitudes of the valve assembly to enhance the accuracy of injection amount of fuel, if the surface roughness R max of the high-hardness coating formed on the valve assembly is about 2 μm, the sliding resistance is increased to bring about a reduction in responsiveness of the valve assembly and an increase in power consumption. Moreover, the wear of the coating advances over a long period, and as a result the opened and closed attitudes of the valve assembly become unstable to exert an adverse effect to the accuracy of the injection amount of fuel. Thus, the performance and the durability of the electromagnetic fuel injection valve cannot be satisfied.